地基极限承载力计算方法及安全判据研究

发布时间：2018-11-15 06:45

【摘要】：近年来,我国的基础建设发展迅猛,其中水利、公路、铁路、机场、港口以及码头等基础设施正在如火如荼的建设。建设这些基础设施时,其地基的极限承载力问题应该首先考虑。目前现有的地基极限承载力计算方法多为半经验公式,且只针对均质土地基。在工程中的地基多为复杂的层状土地基,现有的层状土地基极限承载力的计算方法尚未形成完善的理论体系。本文首先针对目前层状土地基极限承载力计算缺乏准确的计算方法的问题,应用上限解法,建立基于一般滑裂面的层状土地基极限承载力的数值模拟方法;引入单纯形法并结合随机搜索法确定临界滑动模式及最小加载系数,求解极限承载力;并基于Excel内嵌的VBA语言编写地基极限承载力的计算程序以实现较为复杂函数的计算和计算的自动化;通过与现场试验的对比分析证明了本方法及程序的准确性。计算结果与试验结果表明:对于均质土情况，，Vesic方法与本文方法的计算误差最小,误差不足1%, 而Meyerhof以及Terzaghi的方法与上限解的误差最大,均超过20%;对于层状土情况,本文方法与实验结果接近,迈耶霍夫汉纳理论和扩散角法的计算结果与上限解法的计算结果基本吻合,但扩散角法的计算结果更为接近上限解法的计算结果。而利用汉森加权平均公式得出的计算结果与上限解比较相差较大。本文还探讨了应用强度安全系数法对地基进行稳定分析时，安全系数的取值标准。通过工程结构风险分析和可靠度设计方法对上述问题进行解答,计算结果表明其允许安全系数(1.35)应略大于边坡等同类建筑物的相应值。作者将可靠度理论应用于目标可靠度指标为3.7和允许安全系数为1.35的一个典型地基算例,在土的凝聚力和摩擦系数变异系数分别为0.2和0.1的条件下,获得土的凝聚力、摩擦系数的分项系数的值标定值分别为c=1.041, γf=1.418,与国外规范相近。应用陈祖煜等提出的相对安全率判据,可以发现上述的分项系数标定值通过了普适性考核。
[Abstract]:In recent years, the infrastructure of our country is developing rapidly, such as water conservancy, highway, railway, airport, port and wharf. When building these infrastructures, the ultimate bearing capacity of the foundation should be considered first. At present, most of the existing ultimate bearing capacity calculation methods are semi-empirical formula, and only for homogeneous soil foundation. Most of the foundations in engineering are complex layered soil foundations, and the existing calculation methods of ultimate bearing capacity of layered soil foundations have not yet formed a perfect theoretical system. In this paper, aiming at the lack of accurate calculation method for the ultimate bearing capacity of layered soil foundation at present, a numerical simulation method of ultimate bearing capacity of layered soil foundation based on general sliding surface is established by using the upper limit solution. The simplex method and random search method are introduced to determine the critical sliding mode and the minimum loading coefficient to solve the ultimate bearing capacity. The calculation program of the ultimate bearing capacity of foundation is compiled based on the VBA language embedded in Excel to realize the calculation and automation of the complex function, and the accuracy of the method and program is proved by comparing with the field test. The results of calculation and experiment show that for homogeneous soil, the calculation error between Vesic method and this method is the smallest, and the error is less than 1, while the error between Meyerhof and Terzaghi method and upper bound solution is the biggest, both exceeding 20 parts. In the case of layered soil, the present method is close to the experimental results. The results of Meyerhoff Hanna theory and diffusion angle method are in good agreement with those of the upper bound method, but the results of diffusion angle method are closer to those of the upper bound method. However, the calculation results obtained by using Hansen's weighted average formula are quite different from the upper bound solutions. This paper also discusses the criterion of safety factor when using the method of strength safety factor to analyze the stability of foundation. By means of engineering structural risk analysis and reliability design method, the results show that the allowable safety factor (1.35) should be slightly larger than the corresponding value of similar buildings such as slope. The reliability theory is applied to a typical foundation with a target reliability index of 3.7 and a allowable safety factor of 1.35. The coefficient of variation of cohesion and friction coefficient is 0.2 and 0.1, respectively. The values of cohesion and friction coefficient of soil are determined to be c _ (1.041) and 纬 _ f _ (1.418) respectively, which are close to those of foreign specifications. By applying the criterion of relative safety rate proposed by Chen Zuyu et al, it can be found that the calibration values of the above sub-coefficients have passed the universal assessment.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU470

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